While talking with a representative at K&S Engineering I was given a name of a Company that sells retail.They are also in Chicago.
The person I placed my order with was Phil. I am strickly speaking as an objective consumer.

I got some K&S clear plastic sheet a few years ago. It's PETg, or something like that. It's clearer, glossier and more scratch resistant than ordinary acetate or clear styrene - side by side, you can really tell the difference. Aircraft modelers use PETg for thermo-forming canopies.